It is the long-range purpose of this project to study the development of the functions of the small intestine in normal and environmentally, nutritionally, and hormonally-stressed animals. The current functional and toxicological studies that relate to developing and adult animals are: (1) ontogeny of intestinal enzymes and isozymes involved in energy metabolism, i.e., lactate dehydrogenase, NAD-and Fp-glycerol 3-phosphate dehydrogenases, glutamine metabolizing enzymes, gluconeogenic enzymes, and beta-glucuronidase, (2) characterization of the morphology and metabolism of natural and foreing substances in isolated intestinal absorptive cells, and (3) monitoring the response of key intestinal enzymes to in vivo treatments with colon-specific carcinogens, polyhalogenated aromatics and heavy metals.